Now in this article I am focusing about core feature of recyclerView and major used in the current building apps that is Expandable Item in recyclerView. You can expand and collapse the item of recyclerView to see the subitems of particular item. In the old API android provides the ListViewExpandable class the provides the feature to expand and collapse item of group. But in RecyclerView there is no specific Control to handle this.
While implementing this feature I found best library that make my work very simple. But if you want any specific expand feature you can feel free to choose any one as per your requirement.
Here is uploaded video by me that helps you to understand, please check this video.

Lets create the android project to implements the expandable and collapsable item in RecyclerView.
Here are the details of Code that required to achieve this feature.